The present invention relates to a new coal tar pitch and a process for the preparation and use thereof.
During the distillation of coal tar pitch under normal pressure or in vacuo, a soft pitch or normal pitch is obtained as a residue, from which hard pitch is prepared by further distillation and optionally under introduction of a carrier gas or by working in vacuo. In order to adjust the desired properties, various pitches are admixed with each other or with coal tar fractions.
Coal tar pitches contain substances which can be detrimental to health when used in an improper way. One of the most well-known and most tested compounds occurring in coal tar pitch is the carcinogenic benzo[a]pyrene (3,4-benzpyrene). Legislation which has fully taken into consideration the potential dangerousness of this compound, requires that coal tar pitches having a benzo[a]pyrene content (BAP) above 50 ppm (characterized as dangerous substances) must be handled with appropriate care and attention. The BAP-content of normal pitches amounts to from 10,000 to 14,000 ppm. Hard pitches obtained by oxidation or distillation contain from about 4,000 to 12,000 ppm of BAP.
In order to eliminate the health risks caused by improper use of coal tar pitch, this substance has been replaced in several fields by other materials even though these materials have less advantageous properties. Thus other bituminous distillation residues or resins are used. For example, bitumen is used as coal briquets or stones in road construction or phenol resins are used as binding agents in fireproofing.
On the other hand, when coal is subjected to coking a coal tar is formed which has a normal pitch content of about 50% by weight. It is highly desirable to make use of the good properties and high application potential of such pitch while simultaneously decreasing the health risks for humans who handle this substance.